diff --git a/xpcom/glue/nsStringAPI.h b/xpcom/glue/nsStringAPI.h
index a1e941d52675..4072e0e8a679 100644
--- a/xpcom/glue/nsStringAPI.h
+++ b/xpcom/glue/nsStringAPI.h
@@ -116,6 +116,12 @@ public:
   {
     NS_StringSetData(*this, &aChar, 1);
   }
+#ifdef MOZ_USE_CHAR16_WRAPPER
+  NS_HIDDEN_(void) Assign(char16ptr_t aData, size_type aLength = UINT32_MAX)
+  {
+    NS_StringSetData(*this, aData, aLength);
+  }
+#endif
 
   NS_HIDDEN_(void) AssignLiteral(const char *aStr);
   NS_HIDDEN_(void) AssignASCII(const char *aStr) { AssignLiteral(aStr); }
@@ -123,6 +129,9 @@ public:
   NS_HIDDEN_(self_type&) operator=(const self_type& aString) { Assign(aString);   return *this; }
   NS_HIDDEN_(self_type&) operator=(const char_type* aPtr)    { Assign(aPtr);      return *this; }
   NS_HIDDEN_(self_type&) operator=(char_type aChar)          { Assign(aChar);     return *this; }
+#ifdef MOZ_USE_CHAR16_WRAPPER
+  NS_HIDDEN_(self_type&) operator=(char16ptr_t aPtr)         { Assign(aPtr);      return *this; }
+#endif
 
   NS_HIDDEN_(void) Replace( index_type cutStart, size_type cutLength, const char_type* data, size_type length = size_type(-1) )
   {
@@ -224,6 +233,12 @@ public:
   {
     return Equals(other);
   }
+#ifdef MOZ_USE_CHAR16_WRAPPER
+  NS_HIDDEN_(bool) operator == (char16ptr_t other) const
+  {
+    return Equals(other);
+  }
+#endif
 
   NS_HIDDEN_(bool) operator >= (const self_type &other) const
   {
diff --git a/xpcom/io/FileUtilsWin.cpp b/xpcom/io/FileUtilsWin.cpp
index 3e9c5019e1c3..d12ec8b243b9 100644
--- a/xpcom/io/FileUtilsWin.cpp
+++ b/xpcom/io/FileUtilsWin.cpp
@@ -49,7 +49,7 @@ HandleToFilename(HANDLE aHandle, const LARGE_INTEGER& aOffset,
   do {
     mappedFilename.SetLength(mappedFilename.Length() + MAX_PATH);
     len = GetMappedFileNameW(GetCurrentProcess(), view,
-                             mappedFilename.BeginWriting(),
+                             wwc(mappedFilename.BeginWriting()),
                              mappedFilename.Length());
   } while (!len && GetLastError() == ERROR_INSUFFICIENT_BUFFER);
   if (!len) {
diff --git a/xpcom/io/FileUtilsWin.h b/xpcom/io/FileUtilsWin.h
index 01a551fa7a16..dc94e3a7d3b6 100644
--- a/xpcom/io/FileUtilsWin.h
+++ b/xpcom/io/FileUtilsWin.h
@@ -35,7 +35,7 @@ NtPathToDosPath(const nsAString& aNtPath, nsAString& aDosPath)
   nsAutoString logicalDrives;
   DWORD len = 0;
   while(true) {
-    len = GetLogicalDriveStringsW(len, logicalDrives.BeginWriting());
+    len = GetLogicalDriveStringsW(len, reinterpret_cast<wchar_t*>(logicalDrives.BeginWriting()));
     if (!len) {
       return false;
     } else if (len > logicalDrives.Length()) {
@@ -56,7 +56,7 @@ NtPathToDosPath(const nsAString& aNtPath, nsAString& aDosPath)
     DWORD targetPathLen = 0;
     SetLastError(ERROR_SUCCESS);
     while (true) {
-      targetPathLen = QueryDosDeviceW(driveTemplate, targetPath.BeginWriting(),
+      targetPathLen = QueryDosDeviceW(driveTemplate, reinterpret_cast<wchar_t*>(targetPath.BeginWriting()),
                                       targetPath.Length());
       if (targetPathLen || GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
         break;
@@ -68,7 +68,7 @@ NtPathToDosPath(const nsAString& aNtPath, nsAString& aDosPath)
       size_t firstTargetPathLen = wcslen(targetPath.get());
       const char16_t* pathComponent = aNtPath.BeginReading() +
                                       firstTargetPathLen;
-      bool found = _wcsnicmp(aNtPath.BeginReading(), targetPath.get(),
+      bool found = _wcsnicmp(char16ptr_t(aNtPath.BeginReading()), targetPath.get(),
                              firstTargetPathLen) == 0 &&
                    *pathComponent == L'\\';
       if (found) {
diff --git a/xpcom/tests/windows/TestNtPathToDosPath.cpp b/xpcom/tests/windows/TestNtPathToDosPath.cpp
index 4533f7528df1..1f1d75bc41d1 100644
--- a/xpcom/tests/windows/TestNtPathToDosPath.cpp
+++ b/xpcom/tests/windows/TestNtPathToDosPath.cpp
@@ -10,6 +10,8 @@
 #include <winnetwk.h>
 
 #include "mozilla/FileUtilsWin.h"
+#include "mozilla/DebugOnly.h"
+#include "nsCRTGlue.h"
 
 class DriveMapping
 {
@@ -35,8 +37,8 @@ private:
 };
 
 DriveMapping::DriveMapping(const nsAString& aRemoteUNCPath)
-  : mRemoteUNCPath(aRemoteUNCPath)
-  , mDriveLetter(0)
+  : mDriveLetter(0)
+  , mRemoteUNCPath(aRemoteUNCPath)
 {
 }
 
@@ -56,7 +58,7 @@ DriveMapping::DoMapping()
   NETRESOURCEW netRes = {0};
   netRes.dwType = RESOURCETYPE_DISK;
   netRes.lpLocalName = drvTemplate;
-  netRes.lpRemoteName = mRemoteUNCPath.BeginWriting();
+  netRes.lpRemoteName = reinterpret_cast<wchar_t*>(mRemoteUNCPath.BeginWriting());
   wchar_t driveLetter = L'D';
   DWORD result = NO_ERROR;
   do {
@@ -86,7 +88,7 @@ void
 DriveMapping::Disconnect(wchar_t aDriveLetter)
 {
   wchar_t drvTemplate[] = {aDriveLetter, L':', L'\0'};
-  DWORD result = WNetCancelConnection2W(drvTemplate, 0, TRUE);
+  mozilla::DebugOnly<DWORD> result = WNetCancelConnection2W(drvTemplate, 0, TRUE);
   MOZ_ASSERT(result == NO_ERROR);
 }
 
@@ -104,7 +106,7 @@ DriveToNtPath(const wchar_t aDriveLetter, nsAString& aNtPath)
   aNtPath.SetLength(MAX_PATH);
   DWORD pathLen;
   while (true) {
-    pathLen = QueryDosDeviceW(drvTpl, aNtPath.BeginWriting(), aNtPath.Length());
+    pathLen = QueryDosDeviceW(drvTpl, reinterpret_cast<wchar_t*>(aNtPath.BeginWriting()), aNtPath.Length());
     if (pathLen || GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
       break;
     }
@@ -115,7 +117,7 @@ DriveToNtPath(const wchar_t aDriveLetter, nsAString& aNtPath)
   }
   // aNtPath contains embedded NULLs, so we need to figure out the real length
   // via wcslen.
-  aNtPath.SetLength(wcslen(aNtPath.BeginReading()));
+  aNtPath.SetLength(NS_strlen(aNtPath.BeginReading()));
   return true;
 }
 
@@ -191,7 +193,7 @@ int main(int argc, char* argv[])
       fail("Querying network drive");
       return 1;
     }
-    networkPath += L"\\";
+    networkPath += MOZ_UTF16("\\");
     if (!TestNtPathToDosPath(networkPath.get(), expected)) {
       fail("Mapped UNC path");
       result = 1;
@@ -208,7 +210,7 @@ int main(int argc, char* argv[])
       fail("Querying second network drive");
       return 1;
     }
-    networkPath += L"\\";
+    networkPath += MOZ_UTF16("\\");
     if (!TestNtPathToDosPath(networkPath.get(), expected)) {
       fail("Re-mapped UNC path");
       result = 1;